This invention relates to fiber optic cable connectors for coupling a fiber optic cable to related equipment and strain relieving the optical fibers of the cable. More specifically, the invention relates to connectors particularly suited for securing a fiber optic cable to a conventional CATV equipment housing and passing in a strained relieved condition the optical fibers of the cable into the housing for connection to electro-optical componentry.
The use of optical fibers for transmission of CATV signals has numerous advantages over conventional radio frequency (RF) signal transmission through coaxial cable. For example, optical fibers intrinsically have more information carrying capacity than do coaxial cables. In addition, there is less signal attenuation in optical fibers than in coaxial cables adapted for carrying RF signals. Consequently, optical fibers can span much longer distances between signal amplifiers than is possible with coaxial cables. Further, the dielectric nature of optical fiber eliminates any problem with electrical shorting. Finally, optical fiber is immune to ambient electromagnetic interference (EMI) and generates no EMI of its own. Accordingly, fiber optic technology is, more and more, replacing RF technology in the CATV industry.
Conversion to fiber optic technology in the CATV industry is hampered by the significant expense involved with replacing existing RF signal transmission equipment, e.g., coaxial cables, amplifiers and splitters, with fiber optic cables and equipment. As the industry converts to optical fiber technology, it is desirable to utilize existing RF signal equipment to the greatest extent possible to reduce costs. Accordingly, the industry trend is to utilize optical fiber cable for transmitting CATV signals from a centrally located station (headend) over large distances to a number of sub-stations (remote hubs) which may, e.g., be located in various cities. At the remote hubs, the optical signals are reconverted back into RF signals, amplified and split off to relatively short coaxial feeder lines, typically using an optoelectronic bridger amplifier (OEBA). This way, the advantages of optical fiber signal transmission are realized without the expense of replacing the vast networks of coaxial cable and related equipment which bring the CATV signal to individual receiving locations, e.g., residences.
In interest of efficiency, it is desirable to adapt existing CATV equipment housings, e.g., junction boxes, trunk housings and the like, for housing and protecting fiber optic componentry (e.g., OEBA's, amplifiers, splitters, etc.) to which the optic fibers are fed. In such arrangements, it is necessary to secure the end of the fiber optic cable to the equipment housing in such a manner that one or more optical fibers of the cable can pass into the housing and be connected to components therein in a strain-relieved condition. Conventionally, this has been achieved by clamping a strength member of the cable, e.g., Kevlar strands or metal wires, to a floor of the housing such that forces imparted to the cable, e.g., due to the weight of the cable and thermal expansions and contractions thereof, are conveyed to the housing rather than the fragile optical fibers. A problem with this approach for providing strain-relief is that space within the housing must be utilized for securing the cable. Hence, the amount of space available for electro-optical componentry is reduced.
Hopper U.S. Pat. No. 5,074,636 describes a fiber optic cable entry connector which, by securing the cable within the connector exterior of a trunk housing, addresses the above-described problem. This connector is threadably securable in an aperture of the trunk housing and provides strain-relief by grasping a strength member of the fiber optic cable with a screw-actuated clamp positioned within the connector body. The following patents describe other fiber optic cable connectors which capture a strength member of the fiber optic cable in order to provide strain-relief: Corke et al. U.S. Pat. No. 4,948,222; Betzler et al. U.S. Pat. No. 4,815,810; Honma et al. U.S. Pat. No. 4,815,808; Kashimura et al. U.S. Pat. No. 4,730,890; Ejiri et al. U.S. Pat. No. 4,708,427; Ohta et al. U.S. Pat. No. 4,576,437; Borsuk U.S. Pat. No. 4,447,120; and Lumpp et al. U.S. Pat. No. 4,247,163.
Due possibly to such factors as incompatibility with existing CATV equipment, expense, difficulty of installation, size and insufficient strain-relieving strength, the connector designs disclosed in the above patents have not achieved widespread acceptance and usage in the CATV industry. Rather, the industry has continued to rely primarily upon the above-described method of providing strain-relief by securing the fiber optic cable to the floor of the equipment housing, with its attendant disadvantage of taking up space within the housing. There thus exists a need for a fiber optic cable connector which can reliably secure a fiber optic cable to a conventional CATV equipment housing and thereby strain-relieve the optical fibers without taking up housing space, which is inexpensive to manufacture, compact, and can be easily installed.
Conventionally, the individual optical fibers of the cable extending from the connector into the equipment housing for connection to an OEBA or other components are enclosed by a protective "fan-out" tube. Such a tube typically comprises an outer polymeric skin, Kevlar strands acting as a strength member and an inner plastic core for housing and cushioning the individual fibers. None of the above patents addresses the need to strain-relieve the optical fibers from tensile forces imparted to such protective tubing. Conventional practice has been to secure the fan-out tubing to the housing by clamping it to an inner wall portion thereof. This approach also undesirably takes up space within the housing. There is therefore a need for a connector which provides complete strain-relief to the optical fibers by securing therein both a fiber optic cable extending into the connector and a protective tubing covering the individual optical fibers passing out of the connector.